If A and B are both possible causes of E, then when we find that E occurred, providing there are no complicating factors, our beliefs that A occurred and B occurred will both increase.  But if we further discover that A occurred, then our belief that B occurred will go back down a little.  This is called explaining-away, because A provides the explanation for E, and there is no need for B to have occurred to explain E.  Bayes nets automatically handle explaining away in the correct manner, while evidence-based and rule-based systems are generally poor at it.

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